1. Field of the Invention
This invention relates to a driving device for a vibration wave motor, and in particular to a circuit for detecting the amount of deviation between the resonance frequency and the driving frequency of a motor by the use of a phase difference detecting device and stably driving a vibration wave motor.
2. Related Background Art
To drive a vibration wave motor efficiently, it is desired to drive the motor at a mechanical resonance frequency, and a method of providing a monitor electrode for detecting the vibrating state of a motor, and controlling the frequency so that the phase difference between a signal from the electrode and a driving signal becomes constant is proposed in U.S. application Ser. No. 915,429 (filed on Oct. 6, 1986).
Also, to obtain various numbers of revolutions from a motor, it is necessary to drive the motor at other frequencies than the resonance frequency, and it is usual that the motor is driven at frequencies higher than the resonance frequency.
That is, when varying the number of revolutions of the motor, there is adopted a method of arbitrarily setting a frequency higher than the resonance frequency and controlling the number of revolutions of the motor.
When varying the driving frequency in controlling the number of revolutions of the motor by the above-described method, if the variation rate of that frequency is made greater, the number of revolutions can be varied with good responsiveness, while in a state in which that frequency is approximate to said resonance frequency, if the frequency is changed at a great variation rate, there is the fear that the frequency after changed exceeds said resonance frequency and the motor stops and thus stable revolution of the motor becomes impossible.